Back to EveryPatent.com
United States Patent |
5,299,628
|
Ashok
|
April 5, 1994
|
Method and apparatus for the casting of molten metal
Abstract
A method and apparatus for the casting of metal onto a moving horizontal
surface in which the solidification of the casting occurs from the top to
the bottom. The surface on which the metal is cast comprises a material
having a low thermal conductivity of 10 or less watts/meter.degree.
Kelvin. If desired, the casting may be cooled by cooling the top of the
casting at a point downstream of the feeding system.
Inventors:
|
Ashok; Sankaranarayanan (Bethany, CT)
|
Assignee:
|
Olin Corporation (VA)
|
Appl. No.:
|
725867 |
Filed:
|
July 3, 1991 |
Current U.S. Class: |
164/479; 164/429 |
Intern'l Class: |
B22D 011/06 |
Field of Search: |
164/423,463,429,479
|
References Cited
U.S. Patent Documents
4789022 | Dec., 1988 | Ohno | 164/463.
|
Other References
"Introduction to Ceramics" by W. D. Kingery, 1960, John Wiley & Sons, Inc.
p. 490.
|
Primary Examiner: Lin; Kuang Y.
Attorney, Agent or Firm: Burdick; Bruce E.
Claims
What is claimed is:
1. A process for the casting of metal strip comprising:
providing a source of molten metal;
providing a moving unheated substrate for receiving said molten metal
thereon and upon which said metal solidifies as it moves away from said
source, said substrate being selected from a material having a thermal
coefficient sufficiently low that at least 80% of the solidification
occurs progressively in a downward direction starting from the top of the
strip.
2. The process of claim 1 further comprising cooling the top surface of
said cast metal at a point downstream of said source.
3. A process for the casting of metal strip comprising:
providing a source of molten metal;
providing a moving substrate for receiving said molten metal thereon and
upon which said metal solidifies as it moves away from said source, said
substrate being selected from a material having a low thermal coefficient
to minimize cooling from the bottom surface of the metal positioned
against said substrate so that at least 80% of the thickness of the metal
strip is cooled from the top.
4. An apparatus for the casting of metal strip comprising:
a source of molten metal;
a moving unheated substrate for receiving the molten metal thereon; and
means for depositing the molten metal on the substrate and moving said
deposited molten metal away from said source to cause the solidification
thereof, said substrate having a thermal coefficient of 10 or less
watts/meter.degree. Kelvin so that at least 80% of the strip is
progressively solidified in a downward direction.
5. The apparatus of claim 4 further including cooling means for cooling
said cast metal on said substrate, said cooling means being positioned
over the top of said substrate and downstream of said source of molten
metal.
6. The apparatus of claim 4 further including means for preheating said
substrate to a temperature below the melting point of said molten metal
being cast to remove moisture of the system.
7. An apparatus for the casting of metal strip comprising:
a source of molten metal;
a moving unheated substrate for receiving the molten metal thereon; and
means for depositing the molten metal on the substrate and for moving said
molten metal away from said source to cause the solidification thereof,
said substrate having a low thermal coefficient to minimize cooling from
the bottom surface of the metal positioned against said substrate so that
at least 80% of the thickness of the metal strip is cooled from the top.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the casting of metal, and more
particularly, this invention relates to the casting of molten metal onto a
planar area of a continuous moving casting surface such as a continuous
moving substrate.
2. Background Information
The metals industry has been developing a process and apparatus for
producing an as-cast product that needs little or no additional processing
such as hot rolling to reduce it to strip form. One such process that has
arisen as a result of this development is the single belt casting process.
In such a process molten metal is caused to flow onto a moving horizontal
surface such as a continuous belt whereupon it solidifies as it moves
horizontally along with the belt. The solid strip of metal is removed from
the continuous belt for further processing as desired.
In conventional casting utilizing a horizontal moving mold such as a belt,
cooling has typically been provided to the molten metal on the belt from
the bottom side. That is, the cooling has been provided through the belt
against the bottom side of the metal against the belt. In so doing, it has
been noticed that with such type of cooling, porosity may occur in the
middle of the cross-section of the strip. This is thought to be due to the
fact that even though cooling is directed at the bottom side of the strip,
the atmosphere serves to cool the top of the molten metal. Thus, there is
directional solidification from both the top and the bottom of the strip
of metal as it solidifies. This porosity in the middle of the
cross-sectional area of the strip is undesirable in that it cannot be
machined or easily removed. In addition, attempts to provide
unidirectional cooling from the bottom by rapidly cooling the molten strip
from underneath is complicated by the fact that air gaps form between the
strip and the substrate which acts as an insulator.
U.S. Pat. No. 4,789,022 discloses a process for casting metal ribbon having
unidirectional solidification. However, in that patent, it is required to
preheat the substrate to a temperature above the melting point of the
molten metal. Additionally, the process disclosed therein is directed to
the casting of molten ribbon, not strip as contemplated by the present
invention.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide
an improved method of casting onto a planar area of a continuously moving
substrate to form a strip in which the metal strip undergoes
solidification from the top side of the strip, which is the side of the
strip opposite the substrate.
The above and other objects of the present invention may be achieved
through the use of a substrate having a thermal conductivity sufficiently
low to minimize extraction of heat and cooling from the bottom side of the
strip so that at least 80% of the thickness of the strip is cooled from
the top. This may be accomplished by the use of a substrate having a
thermal conductivity of 10 or less watts/meter.degree. Kelvin.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood by reference to the
following detailed description and to the accompanying drawing in which
the FIGURE is a schematic elevational view, partly in section, of a
casting apparatus for use in practicing the present invention.
The present invention is directed to the casting of strip from molten
metal. By strip is meant metal having a rectangular cross-section of
substantially greater width than thickness and in which the thickness is
between about 1/8 to about 3/4 inch and preferably between about 1/4 to
1/2 inch. While the process and apparatus of the present invention may be
applicable to many metals, it is particularly applicable to the casting of
copper and copper alloys.
DETAILED DESCRIPTION
Referring to the drawing, there is shown schematically a casting system
which incorporates the present invention. The molten metal 10 may be
supplied to the casting apparatus 12 from a refractory lined vessel 14
having a discharge opening 16 therein. A plunger 18 is provided in the
interior vessel 14 which is associated with the discharge opening to
control the flow of molten metal from the vessel 14. For this purpose, the
plunger 18 may be vertically reciprocated by any suitable mechanism (not
shown).
A moving substrate 20 having a planar horizontally-disposed surface portion
22 is mounted beneath the discharge opening 16 of the vessel 14. Feeding
means such as a refractory-lined tundish 24 is provided between the vessel
14 and the surface portion 22 in a position to receive the stream 26 of
molten metal issuing from the outlet of the vessel 14. The tundish 24 may
be in the form of a refractory lined trough-like member having a generally
flat inclined bottom 28 with vertical side edges 30. The tundish 24 is
inclined such that its flat or planar bottom surface 28 is inclined
downwardly toward the downstream side of the moving substrate 20 such that
its discharge end is pointing toward the downstream end. With the
arrangement shown, the molten metal stream 26 flows downwardly from the
outlet orifice 16 and impacts against the bottom surface 28 of the tundish
24 and then flows down the inclined bottom surface 28 thereof onto the
surface portion 22 of the moving substrate 20 and solidifies into a strip
32.
In accordance with the present invention, the substrate 20 is fabricated
from a material having low thermal conductivity so that unidirectional
solidification occurs from the top surface downward. The thermal
conductivity of the substrate should be low enough that cooling from the
bottom side of the strip positioned against the substrate is minimized so
that at least 80% of the thickness of the strip is cooled from the top
surface down. In this regard, the substrate should be fabricated from a
material having a thermal coefficient equal to or less than 10
watts/meter.degree. Kelvin. Examples of such materials include high
temperature glasses, such as quartz, and porous ceramics, such as PYROTEK,
made by Pyrotek, Inc. of Carlisle, Pa. By using such a material having a
low thermal coefficient, the extraction of heat through the substrate is
minimized and cooling is substantially accomplished from the top to
bottom.
If desired, the top surface of the casting may be cooled by means of water
jets 34 or the like positioned above the substrate and strip and
positioned downstream of the feeding means. Additionally, should it be
necessary, the substrate 20 may be preheated upstream of the feeding means
24 to remove moisture and organic materials which could cause gas bubbles
during the casting operation. However, the preheating should be to a
temperature substantially less than the melting point of the molten metal
being cast.
The substrate may be in the form of an endless belt such as a caterpillar
drive in which the substrate is in the form of blocks mounted on an
endless chain for movement about spaced rollers. The molten metal is
supplied to the upper run of the drive. The molten metal is carried
forward by the substrate 20 to a point where it is solidified into a
continuous strip. The strip is then separated from the belt and may be
either directly coiled or removed on a roller system for further
processing.
While the invention has been described above with reference to specified
embodiments thereof, it is apparent that many changes, modifications and
variations can be made without departing from the inventive concept
disclosed herein. Accordingly, it is intended to embrace all such changes,
modifications and variations that fall within the spirit and broad scope of
the appended claims. All patent applications, patents and other
publications cited herein are incorporated by reference in their entirety.
Top